1. Field of the Invention
The present invention relates to a linear image sensor IC suitable for a facsimile machine, an image scanner, or the like for reading and transmitting image information, and to a semiconductor device having the linear image sensor IC.
2. Description of the Related Art
In an image sensor, a PN junction is used as a photoelectric conversion device. FIG. 3 is a sectional view illustrating a pixel portion of a conventional image sensor. A PN junction between an N type silicon substrate 1 and a pixel P type diffusion layer 2 is used as a photoelectric conversion device. Light enters a pixel region 10 and impinges on silicon lattice to generate minority carriers. The minority carriers move in the N type silicon substrate 1 and reach the pixel P type diffusion layer 2 to be photoelectrically converted.
By absorbing minority carriers generated in the silicon substrate 1 except the pixel region 10 with a guard ring 8 which is a P type diffusion layer formed so as to surround the pixel region 10, only light which enters the pixel region 10 can be sensed. When the pixel region 10 is adjacent to an edge of a chip, the minority carriers coming from that direction is ignorable and thus, the guard ring 8 can be omitted with regard to that direction. Further a scribe region 11 has an isolation 3 on the substrate 1 and a passivation 4 on the isolation 3. A wire 5 is disposed on the isolation 3 and is connected to the pixel P type diffusion layer 2 and the passivation 4.
However, an image sensor structured as above has a problem in that its characteristics when the sensor is on a wafer are different from those when it becomes a finished product. This is due to difference in the amount of the minority carriers in the respective pixel areas caused by special structures such as an alignment mark on scribe regions or structures of peripheral circuits for adjacent chips.
In order to solve the above problem, according to an aspect of the present invention, a linear image sensor IC is structured as in the following. A linear image sensor IC having no guard ring PN junction between a PN junction for receiving light and an adjacent scribe region is structured such that a silicon substrate surface retaining a silicon substrate impurity concentration appears in the scribe region. Alternatively, a linear image sensor IC is structured such that the scribe region forms a PN junction of a silicon substrate impurity concentration, the PN junction being given no electric potential.
According to another aspect of the present invention, a semiconductor wafer having a linear image sensor IC arranged on a surface thereof, the linear image sensor IC having a PN junction for receiving light and a guard ring spaced from the PN junction, further comprises a scribe region adjacent to the linear image sensor IC on a side opposite to a side of the guard ring, the scribe region having a surface impurity concentration equal to a substrate impurity concentration of the semiconductor wafer. Further, a PN junction of a substrate impurity concentration of the semiconductor wafer is arranged in the scribe region.